Rotating heads for electrostatic atomizing and spraying apparatus



Nov. 13, 1962 AND SPRAYING APPA RATUS Filed March 21, 1960 12a 12 Q h 'wI HIGH L POTENTIAL SOURCE Fig.4"

y W41... fi fl nited fitates The present invention relates toimprovements in rotating electrostatic heads for electrostatic atomizingand spraying apparatus, which comprise in particular a sharp edge forelectric leakage and combine electrical atomizing with atomization bycentrifugal force. As is known, such heads may be employed instationary, movable or portable apparatus for coating objects, accordingto an electrostatic process, with fine particles of materials such aspaints.

Among the factors which influence the technical properties and theappearance of the object which is coated according to this method, onefactor is of prime importance. This is the regular and uniform feedingof paint, which is still in the liquid state in the electrostatic head,towards the spraying edge.

In order that the paint may progress regularly and be regularly atomizedand sprayed, it is necessary to ensure a progressive feeding of thepaint towards the atomizing edge without sudden variation of directionand without reflections from the walls of the head.

Such sudden variations of direction can only add unnecessary resistancesof varying degree which have an adverse effect on the regular flow ofpaint.

Reflections from the walls of the head must be carefully avoided,becausethey may create eddies in the circulation of the paint and theseeddies may cause obstructions, particularly in the case when very heavypaints are utilised, such as red lead, oil paints or zinc oxide paints,etc. Eddies which are produced with such paints may create zones wherethere is no circulation and Where a sedimentation of the paint will beproduced, which will impede or may even block the flow of paint towardsthe atomizing edge.

The invention has for its object to provide improvements inelectrostatic heads by means of which a regular and progressive supplyof paint towards the atomizing edge is ensured.

In order that the invention may be more fully understood, someembodiments thereof will now be described by way of non-limitingexamples, and with reference to the accompanying drawings in which:

FIGURE 1 shows a front view of one embodiment of an improvedelectrostatic head according to the invention.

FIGURE 2 is a longitudinal section along XOY of FIG- URE 1.

FIGURES 3 and 4 are sections, which are similar to that of FIGURE 2, ofmodified embodiments.

Referring to FIGURES 1 and 2, it can be seen that the head 1, whichpreferably has a cylindrical shape, comprises a central part or hub 2,at the centre of which is a housing 2 by means of which the head 1 canbe attached to a member (not shown) which imparts to it its rotarymovement about its axis.

In accordance with the invention, the external surface of the hubcomprises several successive surfaces, flaring progressively relative tothe direction of feeding of the paint, in order to terminate in wideapertures through which said paint flows towards the atomizing edge.

In FIGURE 2 only two such surfaces 2a, 2b are shown externally of thehub and in FIGURE 1 only four such 3,063,642 Patented Nov. 13, 1962apertures are shown, but it is obvious that the numbers indicated are inno Way intended to be limiting.

Preferably, these apertures 3, 4, 5, 6 are inwardly curved, in the arcof a circle about the axis of rotation O of the head. For the samepurpose these apertures have a relatively small radial width in theupstream portion and flare towards the downstream portion in thedirection of flow of the paint. In this manner, circulation towards theatomizing edge is facilitated through the effect of centrifugal force.

The upstream inlet of these apertures is in communication with the paintfeed channel 7 which, owing to the shape of the external surface of thehub 2, offers a minimum of resistance to the flow of paint and moreoverensures a regular feeding of the paint. No eddies due to reflections ofthe paint can be created at any point of this circulation path and thusthe above mentioned drawbacks are avoided.

Such a head, which may be made of metal or of a high resistivitymaterial, has given excellent results during tests. In one particularembodiment, the head is constituted by a high resistivity materialcomprising parts by weight of a thermosetting resin of the ethoxyline orepoxid type and 3 parts of lamp-black, but the invention is obviouslynot limited to this example which is given simply by way ofillustration. This is also true of the geometrical shape of theapertures 3 to 6.

- In the embodiment of FIGURE 3 the head comprises a substantiallyhollow cylindrical external part 11 which is fixed to the hub 12, whoseexternal surface also comprises several successive surfaces 12a, 12b,flaring progressively relative to the direction of paint feed. Thedriving shaft for rotating the head is shown at 13.

In this embodiment the paint is fed through a nozzle 14 which isdirected in such a manner that the paint jet leaving the nozzle makes avery obtuse angle with one of the external surfaces of the hub 12.arrives very obliquely on these walls and this prevents any reflectionof the paint jet on any wall of the head. Therefore, the liquid advancesregularly towards the apertures 15 provided between the hub and theexternal part 11 of the head and thereafter towards the atomizing edge.

In the case when the paint is fed through a nozzle such as 14, in orderto prevent a back-fiow of this paint along the nozzle 14, this nozzle isadvantageously pro vided with an ejector 16, which cooperates indirecting the jet of liquid very obliquely on to the external flaredsurface of the hub 2 and which moreover prevents a moistening of thepaint inflow pipe and consequently avoids a back-flow of the paint.

In FIGURE 3, the inlet nozzle 14 is shown substantially parallel to thelongitudinal axis of the head, but ohviously, it could also be slightlyinclined relative to this axis. The important condition to be fulfilledis that the paint is fed very obliquely on to the external wall of thehub 12, without being subjected to a sudden variation of direction andwithout reflection on any wall of the head.

FIGURE 4 shows a modification, similar to that of FIGURE 3, which isparticularly suitable for heads intended to supply a large output ofpaint. The external part 17 of the head, instead of being cylindricallike the part 11 of FIGURE 3, has a slightly truncated cone shape. Thisshape combined with the external surface of the previously described hub12, enables a film of liquid to be obtained which is thinner than incylindrical heads and avoids any accumulation of paint inside the head.Obviously, it is also possible to provide an ejector 16 as in theprevious embodiment.

I claim:

1. A rotary head for electrostatic atomizing and spraying of a fluid andcombining electrical atomizing with Therefore, the liquid apeaeeaatomization by centrifugal force, comprising a body portion having anedge for electric leakage, a hub within said body portion and surroundedby apertures, said hub comprising plural successive external surfaceswhich progressively flare outwardly towards said body portion atincreasing angles with respect to the axis of rotation of the head andwhich are all inclined at an obtuse angle with respect to said axis ofrotation, means for directing the fluid to be sprayed on to that one ofthose external surfaces adjacent the axis of rotation of the head in adirection substantially parallel to the axis of rotation of said head,at least one external surface of the hub serving as a centrifugalgradient to feed said fluid progressively and without sudden variationsin direction towards the apertures through which it passes to theatomizing edge, and said apertures being arcuately curved and circularlydisposed about the axis of rotation of the head and having a relativelysmall radial width in the upstream portion and flaring towards thedownstream portion in the direction of flow of the fluid.

2. A rotary head for electrostatic atomizing and spraying of a fluid andcombining electrical atomizing with atomization by centrifugal force,comprising a body portion having an edge for electric leakage, a hubwithin said body portion and surrounded by apertures, said hubcomprising plural successive external surfaces which progressive'lyflare outwardly towards said body portion at increasing angles withrespect to the axis of rotation of the head and which are all inclinedat an obtuse angle with respect to said axis of rotation, a fluid inletnozzle for directing the fluid to be sprayed on to that one of thoseexternal surfaces adjacent the axis of rotation of the head in adirection substantially parallel to the axis of rotation of said head,at least one external surface of the hub serving as a centrifugalgradient to feed said fluid progressively and without sudden variationsin direction towards the apertures through which it passes to theatomizing edge, and an ejector provided at the end of the fluid inletnozzle, said ejector including means in order to avoid said hub portioncomprising at least two external surface a back-flow of the fluid on theoutersurface of the nozzle. 40

parts inclined at diiferent and progressively increasing angles withrespect to the axis of said head but which are all inclined at an obtuseangle with respect to said axis and which thus progressively flareoutwardly towards said apertures.

4. In apparatus for electrostatic atomizing and spraying and combiningelectrical atomizing with atomization by centrifugal force for coatingobjects with fine particles of a material such as paint, a rotarygenerally cylindrical head member having an edge for electrical leakage,a hub within said head member comprising several successive externalsurfaces which progressively flare outwardly relative to the directionof feed of the paint jet, said jet being directed on to that one ofthose surfaces adjacent the axis of rotation of the head at asubstantially obtuse angle, at least one surface of the hub serving tofeed this paint regularly towards apertures which finally feed it to theatomizing edge, whereby any sudden variation of direction of the paintand any reflection of the paint on any wall of the head is substantiallyavoided and said apertures being arcuately curved and circularlydisposed about the axis of rotation of the head and having a relativelysmall radial width in the upstream portion and flaring towards thedownstream portion in the direction of flow of the paint.

References Cited in the file of this patent UNITED STATES PATENTS2,926,106 Gauthier Feb. 23, 1960 FOREIGN PATENTS 1,110,350 France Oct.12, 1955

